The present invention relates generally to electric generators, and more particularly to an electric generator assembly contained within a propeller system for a turbo-prop engine.
Turbo-prop engines are known within the aircraft industry and function by ingesting air into a compressor section, which includes alternating sections of rotating blades and stationary vanes. Each blade and vane combination is called a compressor stage, within which the air is successively compressed prior to entering the combustion section. The combustor section injects fuel and ignites the air-fuel mixture. The resulting combustion process produces exhaust gases composed of hot air and combustion products that are expelled and expanded through high pressure and power turbines. The first stage turbine shares a common shaft with the rotating blades within the compressor and provides the motive power to the compressor by extracting energy from the exhaust gases. Similarly, the power turbine drives the propeller assembly through a reduction gearbox by further extracting energy from the exhaust gases, which are expelled from the gas turbine through an exhaust nozzle. The reduction gearbox functions to reduce the shaft speed of the power turbine, producing relatively low-speed, high-torque shaft output for driving the propeller assembly. The propeller assembly includes an arrangement of blades affixed to a rotating hub used to propel an aircraft. The speed of the aircraft is determined by the torque imposed on the power turbine by the exhaust gas and by the load imposed by the propeller. The torque delivered to the power turbine is adjustable by controlling the fuel delivered to the combustion section whereas the load imposed by the propeller is controllable by adjusting the pitch of the propeller blades.
There are several known methods of adjusting the pitch of the propeller blades. One such method involves an electric actuator which attaches to each propeller blade and rotates with the propeller assembly within the rotating hub. Electric power can be provided to the motor from a generator located on the stationary side of the turbo-prop engine and transferred to the rotating propeller assembly through slip ring and brush assemblies known in the aircraft industry. Alternatively, the generator can be located within the hub, power generation resulting from the relative movement of a winding and magnet. With this arrangement, typically, the winding is attached to the exterior of the propeller hub and the magnet is attached to the exterior of the reduction gearbox.
Whether electric power is generated in the stationary or the rotating frame of reference, both techniques have disadvantages. For example, the brushes and slip-rings are subject to wear and require more frequent maintenance than non-contact methods. Moreover, driving the magnet portion of the generator at the rotational speed of the hub relative to the gearbox typically requires very large magnets and windings to provide the power to actuate the blades.
Additionally, electric power can be required for other aircraft functions such as restarting an engine during flight and providing emergency electric power during an engine failure. Restarting an engine requires a large battery system or an auxiliary power unit (APU) to spin the compressor and turbine stages to a speed where combustion can occur and be sustained. Emergency electric power is typically provided through a ram air turbine system or RAT that extends from the aircraft to power a generator. Each system adds weight and complexity to the aircraft.
Reducing the weight and improving the reliability of aircraft continues to be a goal of aircraft manufacturers. Therefore, a need exists to provide a consolidated, reliable electric generator system that can fulfill multiple aircraft functions.